1. Field Of the Invention
This invention relates generally to antennas and more particularly to antennas used in providing direction-dependent radiation patterns. Direction-dependent radiation patterns are used in radar and navigation systems to localize the position of an object relative to the antenna.
2. Description Of the Prior Art
In order to provide a directional radiation pattern, it is known in the prior art to rotate mechanically an antenna emitting a relatively narrow radiation pattern. The radiation pattern thus emitted is a function of the direction of the antenna. The antenna can be rotated periodically thereby producing a radiation pattern in which the direction of the radiation pattern is a function of time. The use of mechanical apparatus to rotate an antenna is costly and requires periodic maintenance, frequently in a relatively inaccessible location.
It is also known in the prior art that an antenna, providing an omnidirectional azimuth-dependent radiation pattern, can be mechanically rotated to produce a radiation pattern in which the amplitude of the radiation pattern in a predetermined direction is a function of time. However, the problems associated with mechanical rotation, described above, as well as the difficulty in the determination of radiation pattern maxima or minima provide an undesirable limitation in the usefulness of this type of antenna.
To avoid problems associated with mechanical rotation of antennas, arrays of antenna elements have been used in the prior art to produce a directional radiation pattern. By varying the phase of the signals driving the antenna elements, the directional radiation pattern can be rotated as a function of time. However, the resolution of the array is severely limited without a large number of individual antenna elements. In addition, the application of appropriate driving signals to the array of antenna elements requires complex electronic equipment.
It is therefore an object of the present invention to provide an improved antenna.
It is another object of the present invention to provide an omnidirectional radiation pattern for determination of accurate position information.
It is still another object of the present invention to provide an omnidirectional radiation pattern for determination of object position information without mechanically moving parts.
It is yet another object of the present invention to provide an omnidirectional radiation pattern in which the phase of the emitted electromagnetic waves are a funtion of the direction from the emitting apparatus.
It is a further object of the present invention to provide an antenna emitting electromagnetic waves having a direction-dependent phase-shift.
It is a more particular object of the present invention to provide an antenna system having a radiation from which the position of an object relative to the antenna system can be determined.
It is another more particular object of the present invention to provide a direction-dependent radiation pattern by introducing into an antenna system dielectric materials whose properties vary as a function of the direction of the emitted electromagnetic waves.